1. Field of the Invention
The present invention relates to a golf club which can adjust an angle thereof, that is, can adjust a fixing angle of a head with respect to a center axis of a shaft.
2. Description of the Conventional Art
With respect to a golf club which is put on the market at the present and can adjust an angle thereof, since the angle adjustment is carried out by temporarily taking a shaft out of a head, and further rotating the shaft, in all cases, the shaft is fixed to the head in a state in which it is rotated at a predetermined angle after the angle adjustment in comparison with before the angle adjustment. However, the shaft is structured such that a shaft vibration frequency at a time of hitting a ball is different subtly in correspondence to a fixing direction with respect to the head. Therefore, in accordance with the prior art, since the shaft vibration frequency is changed by carrying out the angle adjustment, a shaft feeling at a time of hitting the ball is changed. A change of the vibration frequency on the basis of a shaft rotating position is described in the following Table 1.
TABLE 1change of shaft vibration frequency on the basisof angle adjusting positionvibrationshaft: Ashaft: Bshaft: Cfrequencydif-dif-dif-measuringvibrationfer-vibrationfer-vibrationfer-positionfrequencyencefrequencyencefrequencyence 0 degree210±0231±0278±0 90 degree204−6226−5271−7180 degree211+1230−1278±0270 degree206−4227−4272−6maximum657difference
note 1) the difference is a numerical value on the basis of the vibration frequency measuring position of 0 degree.
Further, in the prior art, since the shaft is fixed to the head in a state in which it is rotated, after the angle adjustment in comparison with before the angle adjustment as mentioned above, only a grip having a concentric circular shape can be used as a grip, and it is impossible to use a grip which is provided with a directionality on a circumference having a back line. Therefore, it is hard to firmly grasp the grip, and a design of the grip is constrained.
Further, in the prior art, since it is impossible to apply a sufficient chamfering process to an inner diameter portion of an end surface of a part to which the shaft is inserted, a possibility of a shaft breakage becomes large (refer to patent document 1)
Further, there has been proposed a golf club which can easily adjust an angle thereof without changing a direction on a circumference of a shaft, however, the method includes preparing a plurality of angle adjusting parts and re-bonding the selected parts to the shaft, and it can not be necessarily said that the angle adjustment can be easily achieved (refer to patent document 2).